-LRB- CNN -RRB- -- Aid organizations have deployed emergency response teams to Haiti and appealed for donations after the Caribbean nation was was struck by a devastating earthquake described by local officials as a `` catastrophe of major proportions . ''

The magnitude 7.0 earthquake struck southern Haiti on Tuesday , knocking down buildings and inflicting a new catastrophe on the western hemisphere 's poorest nation .

Humanitarian charity Oxfam said Wednesday it was rushing rescue teams to the country from around the region to provide clean water , sanitation , shelter and emergency supplies and called for donations to fund its efforts .

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`` At this stage it is too early to tell the severity of the earthquake in Haiti , but the early signs are not good with communications down across the country , '' said Jane Cocking , humanitarian director of Oxfam .

Kristie van de Wetering , a former Oxfam employee based in the Haitian capital Port-au-Prince , said the situation in the capital was `` very chaotic '' with many buildings reduced to rubble .

`` We can hear people calling for help from every corner . The aftershocks are ongoing and making people very nervous , '' she said .

The International Federation of Red Cross and Red Crescent Societies said volunteers in Haiti were assisting the injured and supporting hospitals which had been overwhelmed by the disaster .

It said it had enough supplies in Haiti for 3,000 families . Experts in disaster response are due to arrive in the country later Wednesday to coordinate international relief efforts , it said .

`` The most urgent needs at this time are search and rescue , field hospitals , emergency health , water purification , emergency shelter , logistics and telecommunications , '' the group said in a statement .

The quake struck about 15 km -LRB- 10 miles -RRB- southwest of Port-au-Prince shortly before 5 p.m. local time , cutting off communications across much of the country .

`` Port-au-Prince is devastated , lot of deaths . SOS . SOS ... , '' wrote Louise Ivers , the clinical director of medical charity Partners In Health , in an e-mail to the group 's offices in Boston , Massachusetts .

She added : `` Temporary field hospital ... needs supplies , pain meds , bandages . Please help us . ''

Raymond Joseph , Haiti 's ambassador to the U.S. , told CNN 's Wolf Blitzer by telephone that the country was going throug

`` I 'm calling on all friends of Haiti and people who are listening to me to please come to our aid , '' said Raymond Joseph , Haiti 's ambassador to the U.S. told CNN 's Wolf Blitzer by telephone .

`` Today as Haiti is going through the worst day in its history I am calling for all others who got help from us in the beginning to help in support , '' Joseph said . `` The only thing I can do now is pray and hope for the best . ''

Singer Wyclef Jean , nephew of ambassador Joseph , stressed the need for help for what is considered among the poorest nations in the Western Hemisphere .

`` We 're going to need immediate aid , '' Jean told Blitzer on CNN . `` We 're going to need the United States and the international community to react immediately . '' He founded Yele Haiti , whose community service programs include food distribution and emergency relief .

In Washington U.S. President Barack Obama said the government would `` stand ready to assist the people of Haiti . ''

At the Pentagon , the U.S. military said humanitarian aid was being prepared for shipping , but it was not yet clear where or how it would be sent . A U.S. aviation source said the control tower at the Port-au-Prince international airport collapsed , possibly hindering efforts to fly relief supplies into the country .

Secretary of State Hillary Clinton told reporters that Washington is offering `` our full assistance '' to Haiti . `` And our prayers are with the people who have suffered , their families and their loved ones , '' she said . The deputy chief of the U.S. mission in Haiti , David Lindwall , told Clinton that he saw `` significant damage '' from the quake and said U.S. officials there expect `` serious loss of life , '' Crowley said .

And Clinton 's husband , former U.S. President Bill Clinton -- now the U.N. special envoy for Haiti -- said the world body was `` committed to do whatever we can to assist the people of Haiti in their relief , rebuilding and recovery efforts . ''

Haiti 's government is backed by a U.N. peacekeeping mission established after the ouster of former President Jean-Bertrand Aristide in 2004 .

The United States has been heavily involved in Haiti commercially , politically and militarily for most of the last century . U.S. intervention under Clinton restored Aristide to power in 1994 after a 1991 coup , and a U.S. jet hustled him out of the country again in 2004 following a rapidly spreading uprising against his government .

With people stripping the trees for fuel and to clear land for agriculture , the mountainous countryside has been heavily deforested . That has led to severe erosion and left Haitians vulnerable to massive landslides when heavy rains fall .

Roads in Haiti were unsafe to travel on because of a lack of lighting and because many buildings along transportation routes had collapsed or were not deemed safe , said Ian Rodgers of the relief organization Save the Children .

`` What I can hear is very distressed people , '' Rogers said . `` There is a lot of distress and wailing of people trying to find loved ones . ''

A representative for the aid group Catholic Relief Services in Haiti described the situation in the nation as `` a total disaster , '' said Robyn Fieser , regional information officer for the group .

Haiti 's dense population will increase the risk to its people , Jean said . The nation 's need for aid will range from water and food to medical and building supplies .

`` This is the worst devastation that we as Haitian people have faced , '' he said .

Hurricane Gordon killed more than 1,000 people in 1994 , while Hurricane Georges killed more than 400 and destroyed the majority of the country 's crops in 1998 . And in 2004 , Hurricane Jeanne killed more than 3,000 people even as it passed north of Haiti , with most of the deaths in the northwestern city of Gonaives .

Gonaives was hit heavily again in 2008 when four tropical systems passed through .

According to the U.N. Office for the Special Envoy for Haiti , unemployment reaches 70 percent nationally , and 78 percent of Haitians live on less than $ 2 a day .

CNN 's Edvige Jean-Francois , Shasta Darlington , Deb Feyerick , Matt Smith , Mike Mount and Pierre Meilhan contributed to this report .

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`` Temporary field hospital ... needs supplies , pain meds , bandages , '' doctor writes

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U.S. military says humanitarian aid was being prepared for shipping

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Haitian ambassador to the United States describes `` worst day '' in Haitian history

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Save the Children : Lack of lighting , collapsed routes render roads unsafe

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Catholic Relief Services describes situation as `` a total disaster ''